Lenses and optical systems

Abstract

Provided are a lens and an optical system. The lens comprises two lenses. The first lens is a positive meniscus lens comprising a first surface and a second surface. The first surface is convex and faces the object side, and the second surface is concave and faces the image side. The second lens is a negative meniscus lens comprising a third surface and a fourth surface. The third surface is convex and faces the object side, and the fourth surface is concave and faces the image side. The first lens and the second lens are arranged in sequence along the optical axis from the object side to the image side. The lens satisfies 0 < f1 / f < 1 and -3 < f2 / f < -2. Wherein, f is the focal length of the lens, f1 is the focal length of the first lens, and f2 is the focal length of the second lens. In this way, the lens can have lower cost, higher reliability and better portability.

Description

Technical Field

[0001] This application relates to the field of optical components, and more specifically to a lens and an optical system. Background Technology

[0002] Infrared lenses are currently widely used in various monitoring applications, such as forest fire prevention, road monitoring, and airport security. Long-wave infrared lenses are a type of infrared lens and are now widely used. However, most long-wave infrared lenses designed for large-area infrared systems currently employ a three-element structure, resulting in higher costs and a longer overall optical length. Summary of the Invention

[0003] This application is made in view of the state of the prior art described above. The object of this application is to provide a lens and optical system that can overcome at least one of the disadvantages described in the background art.

[0004] To achieve the above objectives, this application adopts the following technical solution.

[0005] This application provides a lens comprising two lenses: a first lens, which is a positive meniscus lens, comprising a first surface and a second surface, the first surface being convex and facing the object side, and the second surface being concave and facing the image side; and a second lens, which is a negative meniscus lens, comprising a third surface and a fourth surface, the third surface being convex and facing the object side, and the fourth surface being concave and facing the image side. The first lens and the second lens are arranged sequentially along the optical axis from the object side to the image side. The lens satisfies the following conditions:

[0006]

[0007]

[0008] Where f is the focal length of the lens, f1 is the focal length of the first lens, and f2 is the focal length of the second lens.

[0009] In one alternative embodiment, at least one of the first surface, the second surface, the third surface, and the fourth surface is an aspherical surface.

[0010] In another alternative, the aspherical surface satisfies

[0011]

[0012] Where z is the sag of a point on the aspherical surface along the optical axis, r is the shortest distance between the point and the optical axis, c is the radius of curvature of the aspherical surface, k is the conic coefficient of the aspherical surface, and α iLet be the aspherical coefficients of the aspherical surface, i be the index of the polynomial terms in the aspherical surface, and N be the total number of polynomial terms in the aspherical surface. The first surface satisfies 50 mm ≤ c ≤ 55 mm, k = 0, α2 = 1.40e-07, α3 = -1.27e-10, α4 = 8.13e-14, α5 = 1.30e-16, α6 = -1.53e-19. The second surface satisfies 70 mm ≤ c ≤ 75 mm, k = 0, α2 = -4.00e-7, α3 = -3.94e-10, α4 = 7.00e-13, α5 = -2.83e-12, α6 = -4.96e-16. The third surface satisfies 85... mm≤c≤90mm, k=0, α2=-4.56e-05, α3=-7.74e-10, α4=-1.46e-09, α5=-2.57e-13, the fourth surface satisfies 65 mm≤c≤70 mm, k=0, α2=-5.24e-05, α3=1.35e-07, α4=-4.92e-09, α5=5.33e-11, α6=-2.58e-13.

[0013] In another alternative, the second surface is a diffraction surface.

[0014] In another alternative scheme, the diffraction surface satisfies

[0015]

[0016] Where Φ is the phase of the diffraction surface, M is the diffraction order of the diffraction surface, and A i Let ρ be the coefficient of each term in the diffraction surface, ρ be the normalized radial aperture coordinate of the diffraction surface, i be the index of the polynomial term in the diffraction surface, N be the total number of polynomial terms in the diffraction surface, and the second surface satisfies M=33, A1=-90.03, A2=-1.8.

[0017] In another alternative, the first lens and / or the second lens are made of chalcogenide glass.

[0018] In another alternative embodiment, the lens has a focal length of 77 mm, an F-number of 1.1, a field of view greater than or equal to 14.3°, an optical length less than or equal to 80 mm, an optical back focal length greater than or equal to 10 mm, and an operating wavelength of 8 μm to 14 μm.

[0019] In another alternative embodiment, the first lens has a thickness of 9.39 mm on the optical axis, the second lens has a thickness of 4.7 mm on the optical axis, and the air gap between the first lens and the second lens on the optical axis is 58.2 mm.

[0020] In another alternative embodiment, a flat glass plate is also included, located on the image side of the second lens, with an air gap of 9 mm between the flat glass plate and the second lens on the optical axis.

[0021] This application also provides an optical system including the lens and photosensitive element described above.

[0022] By employing the above technical solution, the lens can meet the optical system's requirements for optical power, achromatic aberration, and thermal aberration without the aid of a focusing mechanism, thus achieving a passive, thermal-free optical design. This results in a lens with lower cost and higher reliability. Furthermore, compared to existing technologies, the lens has fewer lenses, enhancing its portability and further reducing cost while improving reliability. Attached Figure Description

[0023] Figure 1 A schematic diagram of an optical system according to an embodiment of this application is shown.

[0024] Figure 2 It shows Figure 1 The optical modulation transfer function curve of the lens of the optical system in the figure at 20°C.

[0025] Figure 3 It shows Figure 1 The optical modulation transfer function curve of the lens of the optical system in the figure at -40℃.

[0026] Figure 4 It shows Figure 1 The optical modulation transfer function curve of the lens of the optical system in the figure at 60°C.

[0027] Figure 5 It shows Figure 1 Field curvature diagram of the lens in the optical system.

[0028] Figure 6 It shows Figure 1 The distortion diagram of the lens in the optical system.

[0029] Figure 7 It shows Figure 1 The relative illumination diagram of the lens in the optical system.

[0030] Explanation of reference numerals in the attached figures

[0031] 1. Lens; 11. First lens; 12. Second lens; 13. Flat glass;

[0032] 2. Photosensitive element;

[0033] S1 First side; S2 Second side; S3 Third side; S4 Fourth side;

[0034] A. Optical axis. Detailed Implementation

[0035] Exemplary embodiments of this application are described below with reference to the accompanying drawings. It should be understood that these specific descriptions are for teaching those skilled in the art how to implement this application only, and are not intended to exhaust all possible methods of this application, nor to limit the scope of this application.

[0036] In this application, scientific notation is used to represent some numerical values. For example, 1.40e-07 represents 1.40 × 10⁻⁷. -7 Unless otherwise specified, "from one value to another" includes both the value and the value itself.

[0037] Figure 1 An optical system according to an embodiment of this application is shown, particularly a large target surface optical system, such as a thermal imager.

[0038] Reference Figure 1 The optical system may include a lens 1 and a photosensitive element 2.

[0039] Lens 1 may include a first lens 11, a second lens 12, and a flat glass plate 13. Specifically, lens 1 includes only two lenses. The first lens 11 may be a positive meniscus lens, which may include a first surface S1 and a second surface S2. The first surface S1 may be convex and face the object side, and the second surface S2 may be concave and face the image side. The second lens 12 may be a negative meniscus lens, which may include a third surface S3 and a fourth surface S4. The third surface S3 may be convex and face the object side, and the fourth surface S4 may be concave and face the image side. The first lens 11 and the second lens 12 may be made of chalcogenide glass and have different refractive index temperature coefficients.

[0040] The first lens 11, the second lens 12, and the plate glass 13 can be arranged along the optical axis A. Specifically, the first lens 11 can be located on the object side of the second lens 12, and the plate glass 13 can be located on the image side of the second lens 12. The thickness of the first lens 11 along the optical axis A can be 9.39 mm, and the thickness of the second lens 12 along the optical axis A can be 4.7 mm. The air gap between the first lens 11 and the second lens 12 along the optical axis A can be 58.2 mm, and the air gap between the second lens 12 and the plate glass 13 along the optical axis A can be 9 mm. The total optical length of lens 1 can be less than or equal to 80 mm, and the optical back focal length of lens 1 can be greater than or equal to 10 mm. The F-number of lens 1 can be 1.1, and the field of view of lens 1 can be greater than or equal to 14.3°. The focal length of lens 1 can meet the following requirements.

[0041]

[0042]

[0043] Where f is the focal length of lens 1, f1 is the focal length of the first lens 11, and f2 is the focal length of the second lens 12. For example, the focal length of lens 1 can be 77 mm.

[0044] The first lens 11 and the second lens 12 may include aspherical surfaces. Specifically, the first surface S1, the second surface S2, the third surface S3, and the fourth surface S4 may be aspherical surfaces, and the aspherical surfaces can satisfy the following conditions:

[0045]

[0046] Where z is the sag of a point on the aspherical surface along the optical axis A, r is the shortest distance between the point and the optical axis A, c is the radius of curvature at the vertex of the aspherical surface, k is the conic coefficient of the aspherical surface, and α i Let be the aspherical coefficients of the aspherical surface, i be the index of the polynomial terms in the aspherical surface, and N be the total number of polynomial terms in the aspherical surface. For example, the first surface S1 satisfies 50 mm ≤ c ≤ 55 mm, k = 0, α2 = 1.40e-07, α3 = -1.27e-10, α4 = 8.13e-14, α5 = 1.30e-16, α6 = -1.53e-19; the second surface S2 satisfies 70 mm ≤ c ≤ 75 mm, k = 0, α2 = -4.00e-7, α3 = -3.94e-10, α4 = 7.00e-13, α5 = -2.83e-12, α6 = -4.96e-16; the third surface S3 satisfies 85 mm ≤ c ≤ 90 mm. mm, k=0, α2=-4.56e-05, α3=-7.74e-10, α4=-1.46e-09, α5=-2.57e-13; the fourth surface S4 can satisfy 65 mm≤c≤70 mm, k=0, α2=-5.24e-05, α3=1.35e-07, α4=-4.92e-09, α5=5.33e-11, α6=-2.58e-13. In the above aspherical formula, the coefficient α is not given. i It is 0.

[0047] The first lens 11 may include a diffraction surface. Specifically, the second surface S2 may be a diffraction surface, and the diffraction surface can satisfy...

[0048]

[0049] Where Φ is the phase of the diffraction plane, M is the diffraction order of the diffraction plane, and A iLet ρ be the coefficient of each term in the diffraction plane, ρ be the normalized radial aperture coordinate of the diffraction plane, i be the index of the polynomial term in the diffraction plane, and N be the total number of polynomial terms in the diffraction plane. For example, the second plane S2 can satisfy M=33, A1=-90.03, A2=-1.8. In the above diffraction plane formula, the coefficient A is not given. i It is 0.

[0050] The photosensitive element 2 can be an uncooled long-wave infrared detector. Specifically, the resolution of the photosensitive element 2 can be 1280×1024, and the pixel pitch of the photosensitive element 2 can be 12 μm. The photosensitive element 2 can be positioned on the optical axis A and located on the image side of the flat glass 13. Correspondingly, the operating wavelength of the lens 1 can be from 8 μm to 14 μm.

[0051] Reference Figures 2 to 4 The diagram shows the optical modulation transfer function (MTF) curve of lens 1. The horizontal axis represents spatial frequency, in lines pairs per millimeter (lp / mm). The vertical axis represents the coefficients of the optical transfer function (OTF).

[0052] Reference Figure 2 It shows the meridional (T) and sagittal (S) modulation transfer function curves of lens 1 at 20°C with image plane heights of 0.0000 mm, 2.5000 mm, 4.9000 mm, and 9.8000 mm, and operating wavelengths of 8 μm to 12 μm, under 42 line pairs. From Figure 2 It can be seen that the meridional and sagittal modulation transfer functions of the central field of view (image plane height of 0.0000 mm) are greater than 0.40, while the modulation transfer functions of the other fields of view are greater than 0.33. Lens 1 has higher meridional and sagittal modulation transfer function curves, indicating that lens 1 has better image quality.

[0053] Reference Figure 3 It shows the meridional (T) and sagittal (S) modulation transfer function curves of lens 1 at -40°C, with image plane heights of 0.0000 mm, 2.5000 mm, 4.9000 mm, and 9.8000 mm, and operating wavelengths from 8 μm to 12 μm, under 42 line pairs. From Figure 3 It can be seen that the meridional and sagittal modulation transfer functions of the central field of view (image plane height of 0.0000 mm) are greater than 0.41, while the modulation transfer functions of the other fields of view are greater than 0.27. Lens 1 has higher meridional and sagittal modulation transfer function curves, indicating that lens 1 has better image quality.

[0054] Reference Figure 4It shows the meridional (T) and sagittal (S) modulation transfer function curves of lens 1 at 60°C, with image plane heights of 0.0000 mm, 2.5000 mm, 4.9000 mm, and 9.8000 mm, and operating wavelengths of 8 μm to 12 μm, under 42 line pairs. From Figure 4 It can be seen that the meridional and sagittal modulation transfer functions of the central field of view (image plane height of 0.0000 mm) are greater than 0.41, while the modulation transfer functions of the other fields of view are greater than 0.30. Lens 1 has higher meridional and sagittal modulation transfer function curves, indicating that lens 1 has better image quality.

[0055] Reference Figure 5 The diagram shows the field curvature of lens 1 at operating wavelengths of 8.0000 μm, 8.9218 μm, 10.3897 μm, and 12.0000 μm. The horizontal axis represents the field curvature in mm, and the vertical axis represents the field of view. Curve T is the meridional field curvature, and curve S is the sagittal field curvature. Figure 5 It can be seen that the meridional curvature and sagittal curvature of lens 1 are both controlled within the range of -0.10 mm to 0.10 mm.

[0056] Reference Figure 6 This diagram shows the distortion of lens 1. The horizontal axis represents the percentage of distortion, and the vertical axis represents the field of view. From... Figure 6 It can be seen that the distortion of lens 1 is less than 1.5%, which avoids image distortion and helps to improve the accuracy of information judgment.

[0057] Reference Figure 7 This diagram shows the relative illumination of lens 1. The horizontal axis represents the image plane height of the optical system, in mm. The vertical axis represents the normalized illuminance. From... Figure 7 It can be seen that the center relative illumination of lens 1 is 1, with no energy loss. The edge relative illumination of lens 1 is greater than 0.93. Therefore, the relative illumination of lens 1 is greater than 0.93.

[0058] Thus, with the above configuration, lens 1 can meet the optical system's requirements for optical power, achromatic aberration, and thermal aberration without the aid of a focusing mechanism, achieving a passive, thermal-free optical design. This allows lens 1 to have lower cost and higher reliability. Furthermore, compared to existing technologies, lens 1 has fewer lenses, resulting in better portability; for example, lens 1 can weigh only 150g, further reducing its cost and improving its reliability.

[0059] It should be understood that the above embodiments are merely exemplary and are not intended to limit this application. Those skilled in the art can make various modifications and changes to the above embodiments under the teachings of this application without departing from the scope of this application.

[0060] It should be understood that the first surface S1, the second surface S2, the third surface S3, and the fourth surface S4 are not limited to being aspherical surfaces. In the optional schemes, at least one of them needs to be an aspherical surface.

[0061] It should be understood that the air gap is not limited to being filled with air; it can be filled with any possible gas.

[0062] It should be understood that the radius of curvature at the vertex of the first face S1 is not limited to 50 mm and 55 mm, but may include, for example, 51 mm, 52 mm, 53 mm, and 54 mm. The radius of curvature at the vertex of the second face S2 is not limited to 70 mm and 75 mm, but may include, for example, 71 mm, 72 mm, 73 mm, and 74 mm. The radius of curvature at the vertex of the third face S3 is not limited to 85 mm and 90 mm, but may include, for example, 86 mm, 87 mm, 88 mm, and 89 mm. The radius of curvature at the vertex of the fourth face S4 is not limited to 65 mm and 70 mm, but may include, for example, 66 mm, 67 mm, 68 mm, and 69 mm.

Claims

1. A lens, characterized in that, The focal length of the lens (1) is 77 mm, the F-number of the lens (1) is 1.1, the field of view of the lens (1) is greater than or equal to 14.3°, the total optical length of the lens (1) is less than or equal to 80 mm, the optical back cutoff of the lens (1) is greater than or equal to 10 mm, the working wavelength of the lens (1) is 8 μm to 14 μm, and the lens (1) is composed of a first lens (11) and a second lens (12) arranged sequentially along the optical axis (A) from the object side to the image side. The first lens (11) is a positive meniscus lens. The first lens (11) includes a first surface (S1) and a second surface (S2). The first surface (S1) is convex and faces the object side, and the second surface (S2) is concave and faces the image side. The second lens (12) is a negative meniscus lens. The second lens (12) includes a third surface (S3) and a fourth surface (S4). The third surface (S3) is convex and faces the object side, and the fourth surface (S4) is concave and faces the image side. The lens (1) satisfies Where f is the focal length of the lens (1), f1 is the focal length of the first lens (11), and f2 is the focal length of the second lens (12).

2. The lens according to claim 1, characterized in that, At least one of the first surface (S1), the second surface (S2), the third surface (S3), and the fourth surface (S4) is an aspherical surface.

3. The lens according to claim 2, characterized in that, The aspherical surface satisfies Where z is the sag of a point on the aspherical surface along the optical axis (A), r is the shortest distance between the point and the optical axis (A), c is the radius of curvature of the aspherical surface, k is the conic coefficient of the aspherical surface, and α i Let be the aspherical coefficients of the aspherical surface, i be the index of the polynomial term in the aspherical surface, and N be the total number of polynomial terms in the aspherical surface. The first surface (S1) satisfies 50 mm ≤ c ≤ 55 mm, k = 0, α2 = 1.40e-07, α3 = -1.27e-10, α4 = 8.13e-14, α5 = 1.30e-16, α6 = -1.53e-19. The second surface (S2) satisfies 70 mm ≤ c ≤ 75 mm, k = 0, α2 = -4.00e-7, α3 = -3.94e-10, α4 = 7.00e-13, α5 = -2.83e-12, α6 = -4.96e-16. The third surface (S3) satisfies 85 mm ≤ c ≤ 90 mm, k = 0, α2 = -4.56e-05, α3 = -7.74e-10, α4 = -1.46e-09, α5 = -2.57e-13. The fourth surface (S4) satisfies 65 mm ≤ c ≤ 70 mm, k = 0, α2 = -5.24e-05, α3 = 1.35e-07, α4 = -4.92e-09, α5 = 5.33e-11, α6 = -2.58e-13.

4. The lens according to any one of claims 1 to 3, characterized in that, The second surface (S2) is a diffraction surface.

5. The lens according to claim 4, characterized in that, The diffraction surface satisfies Where Φ is the phase of the diffraction surface, M is the diffraction order of the diffraction surface, and A i Let be the coefficients of each term in the diffraction surface, ρ be the normalized radial aperture coordinates of the diffraction surface, i be the index of the polynomial term in the diffraction surface, and N be the total number of polynomial terms in the diffraction surface. The second face (S2) satisfies M=33, A1=-90.03, A2=-1.

8.

6. The lens according to any one of claims 1 to 3, characterized in that, The first lens (11) and / or the second lens (12) are made of chalcogenide glass.

7. The lens according to any one of claims 1 to 3, characterized in that, The thickness of the first lens (11) on the optical axis (A) is 9.39 mm, the thickness of the second lens (12) on the optical axis (A) is 4.7 mm, and the air gap between the first lens (11) and the second lens (12) on the optical axis (A) is 58.2 mm.

8. The lens according to any one of claims 1 to 3, characterized in that, It also includes a flat glass (13) located on the image side of the second lens (12), and the air gap between the flat glass (13) and the second lens (12) on the optical axis (A) is 9 mm.

9. An optical system, characterized in that, It includes a lens (1) and a photosensitive element (2) as described in any one of claims 1 to 8.

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